1. Field of the Invention
The present invention relates to a single-panel type solid-state imaging device for taking a stereoscopic image.
2. Description Related to the Prior Art
In a single-panel type solid-state imaging device, a color filter array is disposed on a substrate that is formed with a two-dimensional array of photoelectric conversion elements (photodiodes). The color filter array has a plurality of color filters patterned in a mosaic, and each photoelectric conversion element is opposed to the color filter of a specific color. Each pixel, which includes the photoelectric conversion element and the color filter of the specific color, outputs a signal of the specific color corresponding to the color of the color filter, without including signals of the other colors. Accordingly, in order to obtain a multiple-channel image for use in display, it is necessary to perform processing (de-mosaic processing) for obtaining the missing color signals by interpolation from pixels in close vicinity.
In this case, the reproducibility of luminance and color by a high-frequency signal contained in object light becomes a problem. More specifically, a fold-back (aliasing) occurs in the high-frequency signal beyond a reproducible range of each color due to a color pattern of the color filter array, and deteriorates the reproducibility of luminance and color.
A primary-color Bayer pattern is widely used as the color pattern of the color filter array of the single-plate type solid-state imaging device. In the primary-color Bayer pattern, green (G) filters are disposed in a checkered pattern, and red (R) filters and blue (B) filters are evenly disposed in the rest. According to the primary-color Bayer pattern, since the G filters greatly contribute to a luminance signal, the reproducibility of luminance is low in a slanting direction and resolution is low in the slanting direction. In each line extending in a vertical or horizontal direction, only the R filters or only the G filters are disposed in addition to the G filters. Thus, the reproducibility of color is low and may cause a false color.
For this reason, in the single-plate type solid-state imaging device, an optical low-pass filter is disposed on alight entry side of the solid-state imaging device to cut the high-frequency signal from the object light. However, the use of the optical low-pass filter degrades the resolution, and therefore improvement in the color pattern of the color filter array is attempted.
For example, U.S. Pat. No. 6,995,796 proposes a color pattern in which a horizontal array of the R, G, and B filters arranged in a predetermined order is set as a unit and the units are arranged out of phase in a zigzag pattern in the vertical direction, so that every color is present in each and every line extending in any direction (each and every straight line in the horizontal, vertical and slanting directions) in the color filter array.
Also, Japanese Patent Laid-Open Publication No. 08-023543 proposes a color patter in which the R filters and the B filters are disposed in every three pixels in the horizontal and vertical directions and the G filters are disposed therebetween.
According to the color pattern of the U.S. Pat. No. 6,995,796, the presence of every color in each line extending in any direction prevents the occurrence of the false color. However, this color pattern is ineffective at improving the resolution, because this color pattern has the same number of R filters, G filters, and B filters and has a fewer number of G filters than the primary-color Bayer pattern has.
On the contrary, the color pattern of the Japanese Patent Laid-Open Publication No. 08-023543 is effective at improving the resolution because the ratio of the number of the G filters to the number of the R or B filters is higher than that in the case of the primary-color Bayer pattern. However, this color pattern has lines having only the G filters in the horizontal or vertical direction, and hence is ineffective at preventing the false color.
Accordingly, the applicant proposes, in Japanese Patent Application No. 2011-162415, a solid-state imaging device having a color filter array having a color pattern in which the G filters are disposed in each and every line extending in any direction and the R and B filters are disposed in each and every line extending in the horizontal and vertical directions. This color pattern is made by repeatedly disposing a fundamental array pattern of, for example, 6×6 pixels in the horizontal direction and the vertical direction. In the fundamental array pattern, the number of the G filters is more than that of the R or B filters.
Also, there is known a solid-state imaging device in which a pair of pixels (hereinafter called phase difference pixels) that has selectivity in a light entry angle in the horizontal (or vertical) direction is provided in a conventional pixel array having no selectivity in the light entry angle, in order to obtain information about phase difference (parallax) based on pixel values of the phase difference pixels. The information about the phase difference obtained by the phase difference pixels is used in AF processing of a so-called phase difference method, for example.
Furthermore, in recent years, there is proposed a digital camera in which the phase difference pixels are substituted for all pixels so as to obtain a stereoscopic image by using one solid-state imaging device.
In the case of obtaining the stereoscopic image by using the one solid-state imaging device in which the phase difference pixels are substituted for all pixels, right phase difference pixels for selectively receiving light incident from a right side obtain a right-eye image, and left phase difference pixels for selectively receiving light incident from a left side obtain a left-eye image. Thus, it is required to substitute the right phase difference pixels for half of all the pixels, and the left phase difference pixels for the other half. Thus, each of the right-eye image and the left-eye image has low resolution, as compared with an image obtained by a solid-state imaging device in which every pixel is composed of a normal pixel, because the pixel number of the right-eye or the left-eye image is reduced in half. For example, alternately disposing rows of a right phase difference image and rows of a left phase difference image results in reduction of resolution in half in its horizontal direction.
The pixel number of each of the right-eye image and the left-eye image can be interpolated. However, since the original pixel number is low, the interpolation easily causes the occurrence of the false color.